Diabetic coma typically occurs when blood sugar reaches 600 milligrams per deciliter or more, notes WebMD. At-risk individuals typically experience excess thirst and urination for weeks prior to reaching this critical state. These symptoms in addition to extreme blood sugar levels lead to dehydration throughout the body, which may result in shock, coma and death. Death rates can be as high as 40 percent. High-risk individuals include those who are chronically ill or disabled.

A diabetic can work to prevent diabetic coma by getting his blood sugar checked regularly. It is critical for a diabetic to know his target blood sugar ranges and take appropriate action if the readings are out of range. WebMD advises the development of a sick day plan that specifies how often the diabetic checks his blood sugar when sick.